Pes planus, or pes valgo planus, is a deformity producing a severe flat foot. The deformity occurs largely at one particular joint, the talocalcaneal articulation, which is the joint between the talus and calcaneus bones in the foot. There are typically three separate components of a valgus deformity at this joint: first, the calcaneus has a valgus position; second, the head of the talus angulates downward; and third, the forefoot is totally abducted in relation to the hindfoot. In addition, the Achilles tendon may be pulled laterally due to the outward rotation, or eversion, of the calcaneus.
Pes valgo planus often results from the failure of the arch to form in one or both feet of a child aged two to four, which is the typical age for the natural formation of the arch in the foot. The arch may fail to form due to loose joint connections or baby fat lodged between the foot bones of the child. Pes valgo planus also occurs in adults as a result of Posterior Tibial Tendon Dysfunction (PTTD), one of the more common tendon disorders involving the ankle. The posterior tibial tendon helps support the arch of the foot and provides power to point the foot down and to turn the foot inward. PTTD is typically caused by chronic inflammation, degenerative changes, and occasionally trauma, which lead to stretching, laxity, and eventual rupture of the posterior tibial tendon. People suffering from PTTD often experience tenderness and inflammation along the inner part of the ankle, and may experience weakness when standing on their toes. As the disease progresses, the person may experience loss of the arch of the foot while standing, and the foot tends to turn outward under weight. Late stages of the disease are associated with a flat foot deformity with degenerative changes in the joints below the ankle.
In many cases, the symptoms of pes valgo planus may be treated using conservative measures such as anti-inflammatory medications, rest, ice, shoe inserts or orthotic supports, or even ankle-foot braces. However, in some cases, such measures prove inadequate and the person may continue to experience severe foot or ankle pain or suffer from night cramps, pain when walking and/or standing, or lower back and knee pain. In such cases, a subtalar implant may be used to correct the flatfoot deformity while maintaining mobility of the subtalar joint. The subtalar implant is a small device that is inserted into a small opening in the talocalcaneal joint called the sinus tarsi. The placement of the implant restores the arch by preventing the displacement of the talus and by preventing the foot from rolling-in (pronating). In some cases, tissue may grow around the implant which helps hold the implant in place within the sinus tarsi.